ABSTRACT The LRRK2 (leucine-rich repeat protein kinase-2) is mutated in a significant number of Parkinson's disease patients, but little is known about its regulation and function. A common mutation changing Gly2019 to serine enhances catalytic activity, suggesting that small-molecule inhibitors might have utility in treating Parkinson's disease. We employed various approaches to explore the substrate-specificity requirements of LRRK2 and elaborated a peptide substrate termed Nictide, that had 20-fold lower Km and nearly 2-fold higher Vmax than the widely deployed LRRKtide substrate. We demonstrate that LRRK2 has marked preference for phosphorylating threonine over serine. We also observed that several ROCK (Rho kinase) inhibitors such as Y-27632 and H-1152, suppressed LRRK2 with similar potency to which they inhibited ROCK2. In contrast, GSK429286A, a selective ROCK inhibitor, did not significantly inhibit LRRK2. We also identified a mutant LRRK2[A2016T] that was normally active, but resistant to H-1152 and Y-27632, as well as sunitinib, a structurally unrelated multikinase inhibitor that, in contrast with other compounds, suppresses LRRK2, but not ROCK. We have also developed the first sensitive antibody that enables measurement of endogenous LRRK2 protein levels and kinase activity as well as shRNA (short hairpin RNA) methods to reduce LRRK2 expression. Finally, we describe a pharmacological approach to validate whether substrates are phosphorylated by LRRK2 and use this to provide evidence that LRRK2 may not be rate-limiting for the phosphorylation of the proposed substrate moesin. The findings of the present study will aid with the investigation of LRRK2.

[Show abstract][Hide abstract]ABSTRACT: The proteins alpha-synuclein (αSyn) and LRRK2 are both key players in the pathogenesis of the neurodegenerative disorder Parkinson's disease (PD), but establishing a functional link between the two proteins has proven elusive. Research studies for these two proteins have traditionally and justifiably focused in neuronal cells, but recent studies indicate that each protein could play a greater pathological role elsewhere. αSyn is expressed at high levels within neurons, but they also secrete the protein into the extracellular milieu, where it can have broad ranging effects in the nervous system and relevance to disease etiology. Similarly, low neuronal LRRK2 expression and activity suggests that LRRK2-related functions could be more relevant in cells with higher expression, such as brain-resident microglia. Microglia are monocytic immune cells that protect neurons from noxious stimuli, including pathological αSyn species, and microglial activation is believed to contribute to neuroinflammation and neuronal death in PD. Interestingly, both αSyn and LRRK2 can be linked to microglial function. Secreted αSyn can directly activate microglia, and can be taken up by microglia for clearance, while LRRK2 has been implicated in the intrinsic regulation of microglial activation and of lysosomal degradation processes. Based on these observations, the present review will focus on how PD-associated mutations in LRRK2 could potentially alter microglial biology with respect to neuronally-secreted αSyn, resulting in cell dysfunction and neurodegeneration.

[Show abstract][Hide abstract]ABSTRACT: Y-27632 is a well-known inhibitor of the Rho-associated coiled kinase (ROCK) and has been shown to significantly improve the culture of a variety of multipotent stem cell types. However, the effects of Y-27632 on the expansion of adult human adipose-derived stem cell (hADSC) cultures remain to be established. Here, we aimed to characterize the effects of Y-27632 on the culture of hADSCs. Adult hADSCs were isolated from subjects submitted to elective plastic surgery procedures and cultivated in vitro under optimized conditions. Our results show that the continuous supplementation of hADSC cultures with Y-27632 led to decreased numbers of cells and decreased global metabolic viability of hADSC cultures when compared with control conditions. This effect appeared to be dependent on the continuous presence of the drug and was shown to be concentration-dependent and significant for 10 μM and 20 μM of Y-27632. Moreover, the Y-27632-induced decrease in hADSC numbers was not linked to a block in global cell proliferation, as cell numbers consistently increased from the moment of plating until passaging. In addition, Y-27632 was not able to increase the number of hADSCs present in culture 24 hours after passaging. Taken together, our results suggest that, in contrast to other stem cell types, Y-27632 supplementation is not a suitable strategy to enhance hADSC culture expansion.

[Show abstract][Hide abstract]ABSTRACT: In inflammatory demyelinating diseases such as multiple sclerosis (MS), myelin degradation results in loss of axonal function and eventual axonal degeneration. Differentiation of resident oligodendrocyte precursor cells (OPCs) leading to remyelination of denuded axons occurs regularly in early stages of MS but halts as the pathology transitions into progressive MS. Pharmacological potentiation of endogenous OPC maturation and remyelination is now recognized as a promising therapeutic approach for MS. In this study, we analyzed the effects of modulating the Rho-A/Rho-associated kinase (ROCK) signaling pathway, by the use of selective inhibitors of ROCK, on the transformation of OPCs into mature, myelinating oligodendrocytes. Here we demonstrate, with the use of cellular cultures from rodent and human origin, that ROCK inhibition in OPCs results in a significant generation of branches and cell processes in early differentiation stages, followed by accelerated production of myelin protein as an indication of advanced maturation. Furthermore, inhibition of ROCK enhanced myelin formation in cocultures of human OPCs and neurons and remyelination in rat cerebellar tissue explants previously demyelinated with lysolecithin. Our findings indicate that by direct inhibition of this signaling molecule, the OPC differentiation program is activated resulting in morphological and functional cell maturation, myelin formation, and regeneration. Altogether, we show evidence of modulation of the Rho-A/ROCK signaling pathway as a viable target for the induction of remyelination in demyelinating pathologies.

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